Cold-cathode gas tube having a tubular control electrode



June 11, 1968 P. w. STUTSMAN COLD-CATHODE GAS TUBE HAVING A TUBULAR CONTROL ELECTRODE Filed July 1, 1964 FIG. I

FIG. 2

INVENTOR PAUL M. .5 7' UT SMA/V CURRENT AGENT United States Patent "ce 3,388,278 COLD-CATHODE GAS TUBE HAVING A TUBULAR CGNTRGL ELECTRGDE Paul W. Stutsman, Needharn, Mass, assignor to Raytheon Company, Lexington, Mass, a corporation of Delaware Filed July 1, 1964, Ser. No. 379,687 7 Claims. (Q1. 313-197) This invention pertains generally to electric discharge devices, and more particularly to electric discharge devices of the type having an anode, a nonthermionic cathode and a gaseous atmosphere.

Two-element gas ionic discharge devices are common in the electrical arts, and in general they comprise an envelope containing a suitable gaseous medium through which an ionic discharge takes place between an anode and a nonthermionic cathode immersed therein. The ordinary cold-cathode diode is characterized by an apppliedvolts versus current curve which has a rather steep slope for increasing voltage up to a point at which the slope decreases and then changes in sign. The current through the diode at such point of change of sign of the slope of the static characteristic curve is referred to as the critical current, and is a common parameter by means of which tube operation is measured.

In many applications for tubes of this type it is a primary requisite that the critical current be quite low, e.g., on the order of 10* amperes, and requirements such as this have been met in some instances in the prior art, but only at the expense of sacrificing some other desirable characteristic. For example, at least one tube of this general type in the prior art has a critical current on the order of 10* amperes, but this latter tube has relatively poor stability. Unfortunately, a high degree of stability is usually a necessity, along with the requirement for low critical current.

Accordingly, it is a primary object of the present invention to provide a cold-cathode gas tube having the desirable characteristics of the devices of the prior art without the disadvantages thereof.

More specifically, it is an object of this invention to provide a cold-cathode gas tube having an extremely low critical current While maintaining a high degree of stability.

In accordance with the present invention, the above and other objects are achieved by means of a cold-cathode gas-filled electric discharge device including an envelope containing a gaseous medium not nonconductive to highly stable operation, an anode and a cold cathode immersed in the gaseous medium and a tertiary electrode also in the gaseous atmosphere which is operable as a floating potentia member. The distance or spacing between the tertiary electrode and each of the other electrodes is significantly less than the spacing between the anode and the cathode. By means of this construction, low critical current is achieved without the use of nitrogen or other gases which, while affording low critical current, usually result in a lack of stability in tube operation.

With the above considerations and objects in mind, the invention itself will now be described in connection with a preferred embodiment thereof given by way of example and not of limitation, and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a preferred form of the cold-cathode gas tube of the present invention, with portions being broken away,

FIG. 2 is a schematic representation of the elements of the device illustrated in FIG. 1, illustrating a representative relative positioning therebetween, and

FIG. 3 is a graph showing representative static characteristic curves for devices of the type to which this invention pertains.

3,388,278 Patented June 11, 1968 Referring now particularly to FIG. 1, the electric discharge device of the present invention is indicated generally at 10, including an envelope 12 of a suitable ceramic material or other nonconductor and having centrally disposed internal stern members 14 and 16 therein. A cathode electrode 18 is suitably mounted within the supporting stem 16, and an anode electrode 20' is similarly mounted in support member 14, the two electrodes thus being mounted within the tube envelope in substantially coaxial spaced-apart relationship. External leads 22 and 24 are connected, respectively, to cathode 18 and anode 20 to provide respective connections from these electrodes to external circuitry.

A tertiary electrode 26 of substantially tubular or cylindrical form is mounted in substantially coaxial partially telescoping relationship with cathode 18 and anode 20 by means of a pair of mounting straps, one of which is shown at 28 in FIG. 1, the other having been removed for the sake of clarity of description. Strap 28 is mounted on a pair of support rods 30 and 32 which are, in turn, mounted on straps 34 and 36. These latter mounting straps 34 and 36 are positioned, respectively, on the internal stem members 14 and 16 of the envelope 12.

As may be seen in FIG. 1, the distance between cathode 18 and tertiary electrode 26 is much less than the distance between cathode 18 and anode 20. Similarly, the spacing between anode 2i and tertiary electrode 26 is small compared to the spacing between the cathode and the anode. This relative spacing between the three electrodes is believed to play an important role in the operation of the device of the present invention, as will be described.

FIG. 2 shows the device of the present invention in schematic form, including an envelope 33 having a gaseous atmosphere enclosed therein, as indicated by the dot at). Any suitable gaseous atmosphere may be employed, and as was previously stated it will generally be desirable to employ a highly stable gas, such as a mixture of 99 percent neon and 1 percent argon, for example. Obviously, other suitable inert gases or mixtures thereof may be employed, such as krypton, zenon, etc., which gases provide an atmosphere conducive to good stability in the operation of the device.

The device of the present invention may include a radioactive material 42 for use in assisting in obtaining uniform starting potential through ionization and for discharging potential from electrode 56. The material 42 may be supported within the envelope 38 as by being suitably coated or plated on the inner surface of electrode 56. While electrode 56 (or 26) is inteded to be operated at floating potential, an externally extending lead is provided so that a potential on this electrode may be discharged as during tube processing or when desired for rapid discharge of the shield grid potential between successive quantitative tests. The preferred radioactive material for this purpose is nickel 63, although radium may be used in some cases. It was found that AE was lower for tubes containing radium than for those with nickel 63, but nickel 63 appears to be better to insure passing I It is to be understood that although the radioactive material 42 is shown in FIG. 2 as being disposed on the inner surface of shield grid 56, if it is desired a cuplike or other support (not shown) may be provided in encircling relation to the electrodes for supporting the radio-active material. A lead to such a support will provide means for discharging potential on electrode 58 and such a structure would avoid excessive ionization in the space between electrodes 5% and 46.

A cathode 45 is provided with an external lead 48, while the anode 59 has an external lead 52 connected thereto. As was illustrated in FIG. 1, the elongate electrodes 46 and 59 are substantially coaxial, with the gap or spacing therebetween being indicated by the bracket line 54.

Tertiary electrode 56 is substantially cylindrical in form, having slightly flared opposite ends 58 and 60. As shown, tertiary electrode 56 is substantially coaxial with cathode 46 and anode 50, also being disposed in partially telescoping relationship with each of the other electrodes. The spacing between tertiary electrode 56 and the cathode 46 is represented by the bracket 62, and the gap between tertiary electrode 56 and anode 50 is indicated by bracket 64.

A particular requirement of this type of tube is repeatable firing voltage at any given rate of rise of the applied anode voltage through a range of from about 10 to about 1500 volts per second. One specific application, for example, has the requirement that all tubes used in the application fire between 480 and 520 volts, and that no given tube shall fire through a spread of more than about ten volts in this range and with the above rate of rise of the applied anode voltage. Such stability is achieved in the presently described tube, at least in part, by forming the electrodes of molybdenum or zirconium and ageing or seasoning them in the completed tubes until a high degree of gas purity has resulted. Molybdenum and zirconium have exceptionally good gettering properties for gasses except inert gases. The result is a tube having repeatable characteristics under all conditions of use, including long periods of storage.

In the operation of the device illustrated in FIG. 2, it is assumed that the three electrodes 46, 50 and 56 are at a common potential initially. Upon the application of a DC potential between the cathode 46 and the anode i) rendering the latter positive with respect to the former, the anode potential rises to a level almost equal to the breakdown or ionization voltage of gap 64, whereupon the potential of tertiary electrode 56 is correspondingly increased until the breakdown potential of gap 62 is approached. The current in this latter gap produces a space charge of which a portion diffuses to gap 64, causing the current in gap 64 to increase, resulting finally in the ionization of the gap 54.

The mechanism by which the structure of the present invention achieves a desired low critical current without resorting to the use of nitrogen, for example, results from a shift in the static charge configuration produced by a change in the potential of the tertiary electrode 56. Such a change in or disturbance of the space charge conditions can be demonstrated by the deliberate application of a varying signal to a tertiary electrode such as is provided in the device of the present invention; however, it is important to bear in mind that in some cases the tertiary electrode of the present invention has no conductive connection to an external circuit, whereupon the potential of the tertiary electrode is governed by the space charge condition itself, rather than by a deliberately applied external voltage.

A conventional cold-cathode gas discharge diode has a voltage-versus-current static characteristic curve generally in the nature of curve 66 in FIG. 3, wherein potential applied between the anode and cathode is plotted along the ordinate and the resulting current is plotted along the abscissa. As is illustrated by curve 66, a rise in the applied voltage results in an increase in the current from an initial value up to the critical current at point 68. This upward bend of the curve 66 which includes critical current point 68 may be generally referred to as the Townsend region, with the region to the right of the second peak 70 indicating the arc region of operation. The intermediate portion of curve 66 is referred to as the glow region. A pair of load lines 72 and 74 are shown, each representing a different value of resistance in series 'with the diode elements and the source of DC potential.

In the operation of the conventional cold-cathode diode, this static characteristic curve is stationary. Where it is desired to move from one operating point to another, it has been necessary in most of the devices of the prior art to apply a signal in the anode circuit, thus shifting the position of the load line and thereby achieving a different critical current. As will be appreciated by those skilled in the art, the disadvantages incurred in entering the anode circuit with a signal may well outweigh the advantages gained thereby. In accordance with the present invention, the load line is neither shifted in position (as by changiug the anode supply voltage) nor shifted in slope (as by changing the series resistance). Instead, the present invention offers a means for shifting the characteristic curve, while maintaining a fixed load line.

Referring new again to FIG. 3, the shift in the static characteristic curve provided by the device of the present invention is indicated by the displacement between the conventional characteristic curve 66 and the displaced curve 76. Assuming that the series impedance of the energizing circuit corresponds to that of load line 74, it may be seen that the current representative of the point where load line 74 crosses the characteristic curve is reduced from the value I to a materially lower value I For a series resistance represented by the load line 72, the shift of the characteristic curve from 66 to 76 results in an even larger decrease in the current at the point at which the load line crosses the curve, viz., I

As was stated above, the shift of the characteristic curve is believed to be a result of the distortion of the static field resulting from a change in the potential of the tertiary electrode of the device of the present invention, such potential being produced solely by means of the gas discharge and the interelectrode capacity, since no external voltage is applied directly to the tertiary electrode of the device of the present invention.

The invention has been described above in some detail, and particularly with reference to a specific preferred embodiment. However, various detailed modifications not specifically described herein will occur to those skilled in the art. Also, and as apparent in view of the summetry of the device as shown, either of the elements 18 and 20 may serve as the anode, with the other acting as the cathode. Hence, the invention is not to be considered as limited to the particular details given, nor to the specific application to which reference has been made during the description of the device, except insofar as may be required by the scope of the appended claims.

What is claimed is:

1. A cold-cathode gas-filled electric discharge device, comprising a dielectric envelope containing an inert gaseous medium and enclosing a radioactive material, a cathode electrode and an anode electrode mounted within said envelope and defining a space charge region therebetween, each of said electrodes having means connected thereto to provide respective connections external to said envelope, a floating potential tertiary electrode mounted within said envelope and encircling said space charge region, the distance between said tertiary electrode and each of said other electrodes being less than that between said anode and cathode electrodes, and means for applying potential between the cathode and anode electrodes to produce a space charge in said space charge region therebetween, said tertiary electrode being sensitive to said space charge to cause ionization of said gas in the space charge region in response thereto without the aid of external voltage.

2. A cold-cathode gas-filled electrode discharge device, comprising a dielectric envelope containing an inert gaseous medium, a rod-shaped cathode electrode and a rod-shaped anode electrode mounted within said envelope in substantially aligned spaced-apart end-to-end relationship and defining therebetween an interelectrode space means for supporting said cathode and anode electrodes comprising dielectric stem members integral with said envelope extending inwardly thereof toward one another, each of said stem members having portions closely confining portions of the respective cathode and anode electrodes and having tubular-shaped inner end portions encircling said respective electrodes in spaced relation therewith, portions of said electrodes extending toward each other from the open ends of said tubular portions of the stem members, each of said electrodes having means connected thereto to provide respective connections external to said envelope, and a floating potential tertiary electrode mounted within said envelope, the distance between said tertiary electrode and each of said other electrodes being less than that between said anode and cathode electrodes, said tertiary electrode being in substantial coaxial alignment with both said cathode and anode electrodes.

3. A cold-cathode gas-filled electric discharge device, comprising a dielectric envelope containing an inert gaseous medium, a rod-shaped cathode electrode and a rodshaped anode electrode mounted within said envelope in substantially aligned spaced-apart end-to-end relationship and defining therebetween an interelectrode space, means for supporting said cathode and anode electrodes comprising dielectric stern members integral with said envelope and extending inwardly thereof toward one another, each of said stem members having portions closely confining portions of the respective cathode and anode electrodes and having tubular-shaped inner end portions encircling said respective electrodes in spaced relation therewith, portions of said electrodes extending toward each other from the open ends of said tubular portions of the stem members, each of said electrodes having means connected thereto to provide respective connections external to said envelope, and a floating potential tertiary electrode mounted within said envelope, the distance between said tertiary electrode and each of said other electrodes being less than that between said anode and cathode electrodes, said tertiary electrode being in substantial coaxial alignment with both said cathode and anode electrodes and completely surrounding the interelectrode space and adjacent ends of the cathode and anode electrodes.

4. An electric discharge device as set forth in claim 3 wherein said tertiary electrode is tubular in shape and of a length to extend substantially the full distance between the inner ends of said tubular-shaped portions of the stem members.

5. An electric discharge device as set forth in claim 3 wherein radioactive material is fixed to said tertiary electrode.

6. A cold-cathode gas-filled electric discharge device, comprising an envelope containing an inert gaseous medium, a rod-shaped cathode electrode and a rod shaped anode electrode mounted within said envelope is substantially coaxial spaced-apart end-to-end relationship and defining therebetween an interelectrode space, each of said electrodes having means connected thereto to provide respective connections external to said envelope, and a floating potential tertiary electrode mounted within said envelope, the distance between said tertiary electrode and each of said other electrodes being less than that between said anode and cathode electrodes, said tertiary electrode being tubular in form and disposed in substantially coaxial partially telescoping relationship with said cathode and anode electrodes and completely surrounding said interelectrode space.

7. A cold-cathode gas-filled electric discharge device, comprising an envelope containing a mixture of neon and argon gases, a rod-shaped cathode electrode and a rodshaped anode electrode mounted within said envelope in substantially coaxial spaced-apart end-to-end relationship and defining therebetween an interelectrode space, each of said electrodes having means connected thereto to provide respective connections external to said envelope, and a tertiary electrode mounted within said envelope, the distance between said tertiary electrode and each of said other electrodes being less than that between said anode and cathode electrodes, said tertiary electrode being tubular in form and disposed in substantially coaxial partially telescoping spaced relationship with said cathode and anode electrodes and completely surrounding said interelectrode space.

References Cited UNITED STATES PATENTS 2,607,902 8/ 1952 Townsend 313185 X 2,747,121 5/1956 Silver 313-54 2,920,224 1/1960 Back 313-197 3,005,924 10/1961 Reilly 313205 X 3,183,392 5/1965 Craker 313-188 JAMES W. LAWRENCE, Primary Examiner.

STANLEY D. SCHLOSSER, Examiner. 

1. A COLD-CATHODE GAS-FILLED ELECTRIC DISCHARGE DEVICE, COMPRISING A DIELECTRIC ENVELOPE CONTAINING AN INERT GASEOUS MEDIUM AND ENCLOSING A RADIOACTIVE MATERIAL, A CATHODE ELECTRODE AND AN ANODE ELECTRODE MOUNTED WITHIN SAID ENVELOPE AND DEFINING A SPACE CHARGE REGION THEREBETWEEN, EACH OF SAID ELECTRODES HAVING MEANS CONNECTED THERETO TO PROVIDE RESPECTIVE CONNECTIONS EXTERNAL TO SAID ENVELOPE, A FLOATING POTENTIAL TERTIARY ELECTRODE MOUNTED WITHIN SAID ENVELOPE AND ENCIRCLING SAID SPACE CHARGE REGION, THE DISTANCE BETWEEN SAID TERTIARY ELECTRODE AND EACH OF SAID OTHER ELECTRODES BEING LESS THAN THAT BETWEEN SAID ANODE AND CATHODE ELECTRODES, AND MEANS FOR APPLYING POTENTIAL BETWEEN THE CATHODE AND ANODE ELECTRODES TO PRODUCE A SPACE CHARGE IN SAID SPACE CHARGE REGION THEREBETWEEN, SAID TERTIARY ELECTRODE BEING SENSITIVE TO SAID SPACE CHARGE TO CAUSE IONIZATION OF SAID GAS IN THE SPACE CHARGE REGION IN RESPONSE THERETO WITHOUT THE AID OF EXTERNAL VOLTAGE. 